Dicyandiamide-formaldehyde resinous compositions



Patented July 9, 1940 UNITED STATES PATENT OFFICE DICYANDIAMlDE-FORMALDEHYDE RESINOUS COMPOSITIONS KurtRipper, Vienna, Austria, assignor to Ameri can Cyanamid Company, New York, N. Y., a

corporation of Maine 3 Claims.

The invention relates to the production of artificial resins, molding compositions and artificial masses by the condensation of dicyandiamide with formaldehyde.

According to the German patents to Wallasch No. 323,665 and No. 325,647 of 1919, the condensation of dicyandiamide and formaldehyde in the presence of acids, or without any condensing agents, yields oily or glue-like products which may be used as a substitute for glycerine or as water soluble adhesives.

In my prior Patent 1,812,374, I have described the reaction of dicyandiamide and formaldehyde by which it is possible to obtain resinous condensation products capable of. being hardened under the combined or separate action of heat and pressure and convertible into infusible artificlal masses. The condensation products of di cyandiamide and formaldehyde thus produced, when heated for a sufficiently long time, are hydrophobe resins which, on cooling separate from the reaction mixture, and when contacted with water are disintegrated into a powder which dies rapidly. This powder isan excellent molding material in the dry state.

In my British Patent 287,177 I have described a process of making a resin-like condensation product from formaldehyde and dicyandiamide and other materials such as urea, thiourea, phenols or cresols, which are themselves capable of resinfication with formaldehyde. The mixed colloids produced according to this method have properties analogous tothose of the resin obtained by reacting dicyandiamide alone with formaldehyde.

In my British Patent 323,047, I have described a process by which artificial masses are made from dicyandiamide, formaldehyde and a protein substance. This process may be carried out with or without the use of acid or alkaline condensing agents, and yields chiefly molding compositions for hot pressing.

Still another way of making a heat hardenable artificial resin from dicyandiamide and formaldehyde is described in my British Patent 314,359. Under the mild working conditions of this process (a short heating at less than 100 C.) hydrophile condensation products are obtained which on cooling remain dissolved in the reaction mixture. An evaporation process is employed to separate this resin from the solution in which it is generated.

The immediate formation of hydrophobe reaction products has many advantages, not only with respect to the production of the resins and their further treatment, but also in view of the quality of the final product. These hydrophobe resins possess many of the properties which are of importance for the manufacture of quick molding compositions. They can, for instance, as stable colloidal solutions be brought into a state of high and perfectly uniform polymerization by continued heating and in this liquid phase they can be mixed with fibres and fillers to give a homogeneous mass. As a result the hot pressing need serve only for the purpose of mechanical shaping. These materials in their highest state of polymerization are still capable of flowing provided a small amount of water is permitted to remain after the drying process has been completed. The drying of these resins is easily accomplished because of their hydrophobe character.

The present invention relates to a process of improving the water-resistance of the hydrophobe dicyandiamide resins described above. I have discovered that when the dicyandiamideformaldehyde reaction is carried out at a hydrogen ion concentration which is slightly above neutrality (pH 7) a hydgroscopic substance, dicyandiamidine, is produced which in the final product unfavorably affects the water resistance. Thus, when the reaction between dicyandiamide and commercial formaldehyde is carried out without condensing agents, the normal slight acidity of the commercial formaldehyde permits the formation of dicyandiamidine which carries over into the final product.

According to my present invention, the con- I densation of dicyandiamide and formaldehyde is carried out at a lower hydrogen ion concentration than that corresponding to the value of pH 5,

preferably at a hydrogen ion concentration between pH 8 and pH 10. When this is done a hydrophobe resin is obtained which is most appropriate for the manufacture of molding compositions. In addition the condensation takes place very rapidly within the stated hydrogen from which on cooling a tough hydrophobe resin is precipitated. For the further treatment the hydrophobe resin may be caused to separate out either by allowing the mixture to cool down or by the addition of water, whereai'ter it is washed, then melted again and mixed with fibrous material of any convenient kind (of vegetable, animal or mineral origin). Alternately, if a test shows that the hydrophobe resin, precipitating on cooling, has already been formed, the reaction mixture may in the hot condition be lmixed with fibrous materials in a kneading machine or in a roller mill. In both cases the mixture is then treated by heat until the. required degree of polymerisation has been achieved, whereat it becomes dry, and finally subjected to the combined or separate action of heat and pressure.

The condensation may also be carried out at temperatures below the boiling point of the formaldehyde solution. On the other hand it may advantageously be effected under increased pressure.

Moreover I have found, that the quality of the final products may further be improved to a noticeable degree by incorporating metal salts with the condensation products or with the molding powders, for instance copper sulphate, zinc chloride, nitrate of lead, nickel sulphate, cobaltous chloride, aluminium sulphate, stannous chloride, barium chloride or mercury chloride. The effect of these additions is most likely due to the fact that the dicyandiamidine, which may have been formed in spite of the above described operating conditions is bound thereby. It may also be assumed, that these salts exercise besides an assisting coagulating action.

Exmm: I

84 grammes of dicyandiamide are dissolved in 150 grammes of a 30% formaldehyde solution (which proportions correspond to a relation of 1 mol of dicyandiamide to 1%. mols of formaldehyde), whereafter 20 cubic-centimeters of a 0.1 N solution of caustic soda are added. This mixture is now boiled for three quarters of an hour. After this time a high hydrophobe resin, precipitating in the cold, will have been generated. The solution is without preliminary cooling mixed in a kneading machine with 84 grammes of cellulose, either in vacuo or not.

The mixture thus obtained is for the purpose of polymerizing and drying heated, if preferred in two stages of temperature, care being taken to have enough water remain so, that suflicient flowing quality within the hot press is ensured thereby. The final content of water most suitable for this purpose amounts to about 5 per cent. Thereafter any convenient quantities and any kind of pigments or coloring substances may be incorporated with the mass.

In this manner there are obtained molding compositions furnishing by a short hot pressing molded pieces which, when kept in water for a prolonged time, take up very small traces thereof and are adapted therefore for various electrotechnical and other industrial purposes.

EXAMPLE DZ 63 grammes of dicyandiamide are dissolved in 150 grammes of a 30 per cent formaldehyde solution (these proportions corresponding to a relation of 1 mol of dicyandiamide to 2 mols of formaldehyde) and after addition of 40 cubic centimeters of a 0.1 N solution of caustic soda maintained during one hour and three quarters at a temperature of about 80 C. The further treatment is the same as set forth in Example I.

Exams: III

1.16 grammes of boric acid and 10 cubic centimeters of a normal solution of caustic soda are dissolved in 300 cubic centimeters of a 30% aqueous formaldehyde solution. Thereafter 84 grammes of dicyandiamide are added, which amount corresponds to a relation of 1 mol of dicyandiamide to 3 mole of formaldehyde.

The hydrogen ion concentration adjusted by this buffering mixture consisting of borate and sodium hydroxide corresponds toa pH of about 9.4.

The condensation is carried out exactly in the same manner as has been described in the Examples I and II.

Into the molding compositions produced according to the Examples I to I11, together with the pigment for instance 1 to 2 per cent of stannous chloride may be introduced.

Instead of a molding composition for hot pressing a composition suitable for being pressed in the cold may be prepared by continuing the polymerisation and the drying only so'far that a mass is obtained, which permits molding at lower temperatures, the final polymerisation and drying being in such a case effected after the molding.

Instead of a homogeneous molding composition also laminated sheets may be made by impregnating paper or fabrics of any kind with the reaction solution in its initial or final state and uniting a number of these paper sheets or fabrics, after drying and polymerisation of the binding agent, by hot pressing in a plate press.

Instead of the dicyandiamide, derivatives of the same, as well as its raw aqueous solutions, can be used, and instead of the formaldehyde, its polymers can be used.

This application is a division of my copending application, Serial No. 549,798, filed July 9, 1931, now Patent No. 2,060,122.

What I claim is:

1. A composition comprising a hydrophobe resinous reaction product obtained from dicyandiamide and formaldehyde as the essential reactants, and a metal salt selected from the group consisting of copper sulphate, zinc chloride, lead nitrate, nickel sulphate, cobaltous chloride, aluminum sulphate, stannous chloride, barium chloride and mercury chloride.

2. The process of reacting dicyandiamide and formaldehyde to give a hydrophobe resinous product capable of being hardened, under the influence of heat and pressure, into a relatively water insensible finished material which comprises initiating the reaction by heating a solution in which dicyandiamide and formaldehyde are the principal ingredients in the presence of a substance having alkaline properties sufficient to provide a pH of at least 5 and continuing the reaction until the hydrophobe resinous product, capable of separating from the resultant solution on cooling, is formed and adding a metal salt selected from the group consisting of copper sulphate, zinc chloride, lead nitrate, nickel sulphate, cobaltous chloride, aluminium sulphate, stannous chloride, barium chloride and mercury chloride.

3. The process of making a hydrophobe resinous product capable of being hardened under the influence of heat and pressure to give a water insensible finished material which comprises appreciably sensible to water'and adding a metal salt selected from the group consisting of copper sulphate, zinc chloride, lead nitrate, nickel sulphate, cobaltous chloride, alminium sulphate,

stannous chloride, barium chloride and mercury 5 cruel-1:16

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